14 Apr 2010, 11:32am
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by admin

Younger Dryas Megafauna Extinction Comet Theory Discounted

Clovis Mammoth Hunters: Out With a Whimper or a Bang?

ScienceDaily, Apr. 12, 2010, [here]

A team of researchers from the University of Arizona has revisited evidence pointing to a cataclysmic event thought by many scientists to have wiped out the North American megafauna — such as mammoths, saber tooth cats, giant ground sloths and Dire wolves — along with the Clovis hunter-gatherer culture some 13,000 years ago.

The team obtained their findings following an unusual, multidisciplinary approach and published them in the Proceedings of the National Academy of Sciences (PNAS).

“The idea of an extraterrestrial impact driving the Pleistocene extinction event has recently caused a stir in the scientific community,” said C. Vance Haynes, a professor emeritus at UA’s School of Anthropology and the department of geosciences, who is the study’s lead author. “We systematically revisited the evidence for an impact scenario and discovered it just does not hold up.” …

When the last ice age came to an end approximately 13,000 years ago and the glaciers covering a large portion of the North American continent began melting and retreating toward the north, a sudden cooling period known as the “Big Freeze” or, more scientifically, the Younger Dryas, reversed the warming process and caused glaciers to expand again. Even though this cooling period lasted only for 1,300 years, a blink of an eye in geologic timeframes, it witnessed the disappearance of an entire fauna of large mammals.

The big question, according to Haynes, is ‘Why did those animals go extinct in a very short geological timeframe?’”

“When you go out and look at the sediments deposited during that time, you see this black layer we call the Black Mat. It contains the fossilized remains of a massive algae bloom, indicating a short period of water table rise and cool climate that kept the moisture in the soil. Below the Black Mat, you find all kinds of fossils from mammoths, bison, mastodons, Dire wolves and so forth, but when you look right above it — nothing.”

Scientists have suggested several scenarios to account for the rapid Pleistocene extinction event. Some ascribe it to the rapid shift toward a cooler and dryer during the “Big Freeze,” causing widespread droughts.

Haynes disagrees. “We find evidence of big changes in climate throughout the geologic record that were not associated with widespread extinctions.” …

The two attempts to account for the mass extinction event prevailing at this point include humans and celestial bodies. Many deem it possible that humans such as the Clovis culture hunted the Pleistocene mammals to extinction, as proposed by UA Professor Emeritus Paul S. Martin [here].

Alternatively, it is thought that a comet or asteroid slammed into the glaciers covering the Great Lakes area, unleashing firestorms that consumed large portions of vegetation. In addition, the dust and molten rock kicked up high into the atmosphere during the impact could have shrouded the Earth in a nuclear winter-like blanket of airborne dust, blocking sunlight and causing temperatures to plummet. …

“Something happened 13,000 years ago that we do not understand,” said Haynes. “What we can say, though, is that all of the evidence put forth in support of the impact scenario can be sufficiently explained by earthly causes such as climate change, overhunting or a combination of both.”

Does this mean the results obtained by Haynes and his coworkers rule out the possibility of a cosmic event?

“No, it doesn’t,” Haynes said. “It just doesn’t make it very likely.” … [more]

14 May 2010, 6:38pm
by Warren

The cause of the Black Mat was a global flood, which followed the mass extinction. The reason that there is no fossils for a period of time thereafter the global flood is that there was no life in the waters to leave fossil remains.

14 May 2010, 8:35pm
by Mike

That’s one conjecture.

17 Jul 2010, 7:26am
by TT

- What was the cause of this flood?
- A flood alone could not cause all these extinctions?

Reply: There was no global flood, but a series of regional floods before the Younger Dryas (but after the Older Dryas). The Dryases were glacial stadials, i.e. cold periods. A warm period between them, from ~15,000 to 13,500 BP, was when much of the continental ice sheets melted.

There was no single catastrophic flood. The Bretz floods that drained Glacial Lake Missoula occurred as many as 50 times over a period of 1,500 years. That factoid tends to disprove the single comet impact theory.

Nor were the floods everywhere. Plenty of now-extinct megafauna lived where there were no floods. So floods, warming, etc. are not satisfactory explanations for the extinctions. Human hunting most probably played a significant role.



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